Afterdepolarization

A phenomenon in cardiac electrophysiology

Afterdepolarization refers to a phenomenon in cardiac electrophysiology where abnormal depolarizations occur during or after the repolarization phase of the cardiac action potential. These can lead to cardiac arrhythmias and are classified into early and delayed afterdepolarizations.

Types

Early Afterdepolarizations (EADs)

Early afterdepolarizations occur during the repolarization phase of the cardiac action potential, specifically during phases 2 or 3. They are often associated with conditions that prolong the action potential duration, such as long QT syndrome. EADs can lead to torsades de pointes, a type of polymorphic ventricular tachycardia.

Delayed Afterdepolarizations (DADs)

Delayed afterdepolarizations occur after the completion of repolarization, during phase 4 of the cardiac action potential. They are typically associated with increased intracellular calcium levels and can be triggered by conditions such as digitalis toxicity or catecholaminergic polymorphic ventricular tachycardia.

Mechanisms

The mechanisms underlying afterdepolarizations involve complex interactions between ionic currents and intracellular calcium handling.

Ionic Currents

In EADs, the reactivation of L-type calcium channels or persistent sodium channels can contribute to the depolarization. In DADs, the spontaneous release of calcium from the sarcoplasmic reticulum can activate the sodium-calcium exchanger, leading to depolarization.

Calcium Handling

Abnormal calcium handling plays a crucial role in both EADs and DADs. In DADs, the overload of calcium in the sarcoplasmic reticulum can lead to spontaneous calcium release, which then triggers depolarization through the sodium-calcium exchanger.

Clinical Significance

Afterdepolarizations are significant because they can lead to arrhythmias, which are abnormal heart rhythms that can be life-threatening. Understanding the mechanisms of afterdepolarizations is important for developing treatments for arrhythmias.

Related pages

• Cardiac action potential
• Arrhythmia
• Long QT syndrome
• Torsades de pointes

Gallery

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  Illustration of mechanisms of arrhythmia, including afterdepolarizations.